The disclosure of the following priority application is herein incorporated by reference in its entirety: Japanese Patent Application No. 2000-19179 filed Jan. 27, 2000.
1. Field of Invention
The present invention relates to a mask having patterns that are projected by a pair of projection optical systems, and to scanning type exposure apparatus and scanning exposure methods that simultaneously move the mask and a substrate in a predetermined (scanning) direction and that expose images of the patterns formed on the mask onto the substrate.
2. Description of Related Art
In recent years, the use of liquid crystal display panels as a display device of personal computers and televisions, e.g., is rapidly increasing. Such liquid crystal display panels are produced by patterning thin film transparent electrodes, in a desired shape using photolithography techniques, onto a photosensitive substrate having a flat rectangular shape. For such photolithography apparatus, an exposure apparatus is used for exposing images of patterns formed on the mask (reticle) onto the photoresist layer of a photosensitive substrate through projection optical systems.
Meanwhile, efforts are being made to enlarge the aforementioned liquid crystal display panels to provide improved viewing quality. Some scanning type exposure apparatus are known to meet the need for enlargement of the display. Such an apparatus is disclosed in Japanese Laid Open Patent Publication No. 7-57986 (and in U.S. Pat. No. 5,729,331), which has a plurality of projection optical systems that project images of patterns of the mask onto a glass plate substrate as an erect image, while simultaneously moving the mask and the substrate in a predetermined (scanning) direction. Due to the use of the plurality of projection optical systems, this apparatus has a large exposure area in the direction perpendicular to the scanning direction, and sequentially transfers patterns such as an LCD (liquid crystal display) pattern that is formed on the mask onto the exposure area of the glass plate substrate.
In order to achieve a large projection area and superior imaging characteristics without requiring a large projection optical system, the exposure apparatus includes a plurality of (smaller) projection optical systems arranged in such a manner that the projection areas of adjacent projection optical systems are displaced by a predetermined amount in the scanning direction, and also are spaced from each other in the direction perpendicular to the scanning direction such that edge sections of each adjacent projection area overlap in the direction perpendicular to the scanning direction. In this case, a field stop of each projection optical system has a trapezoidal shape and is designed in such a manner that the sum of the aperture width of the field stops in the scanning direction is always equal. For this reason, a scanning exposure apparatus such as described above has a merit in that the portions of exposure areas of the adjacent projection optical systems which join each other are exposed overlappingly, and therefore optical aberration as well as exposure illuminance (exposure light-intensity) change gradually.
In this type of scanning exposure apparatus, in order to control with a high degree of accuracy, the relationship between relative positions of a mask and a substrate during scanning exposure, the relative positions and postures of the mask and the substrate are monitored using a plurality of position measuring instruments such as laser interferometers. These instruments measure the relative position shift of a mask stage which holds the mask and a substrate stage which holds the substrate with respect to the scanning direction (X direction) and with respect to the non-scanning direction (Y direction), which is perpendicular to the scanning direction. The instruments also measure the relative angle shift of the exposure beam with respect to the optical axis (Z direction).
Of these relative position shifts, the relative position shift with respect to the Y direction is obtained by providing long reflection mirrors that extend in the scanning direction (hereafter long mirrors) for the mask stage and for the substrate stage, and by measuring, with interferometers, respective displacement between each stage and its corresponding reflection mirror. In this way, the long mirrors serve as a reference in measuring relative position shift with respect to the Y direction. However, the production cost of long mirrors increases sharply because a high flatness tolerance must be maintained for the entire scanning length of each long mirror.
For this reason, a technology such as disclosed in Japanese Laid Open Patent Publication No. 8-184113 aims to execute scanning exposure without requiring strict flatness tolerance of the long mirrors by ignoring the relative position shift of the mask and the substrate in the Y direction. However, this technology fails when the long mirrors have a waviness with a short period.
Technologies such as disclosed in Japanese Laid Open Patent Publications Nos. 10-284416 and 11-132762 attempt to resolve the aforementioned inconvenience. In these publications, in addition to interferometers that respectively measure the displacement of each stage relative to its corresponding long mirror, a differential type of interferometer is provided for measuring, through long mirrors, relative position shift of the mask stage and the substrate stage in the Y direction. A flatness tolerance of each long mirror is determined by displacing each stage in the X direction and then taking measurements for each stage using each long mirror at two separated locations in the X direction. Based on the result of these measurements, the relative position shift between the mask and the glass plate is corrected.
However, conventional scanning exposure apparatus and scanning exposure method have the following problems. Interferometers are expensive, and due to the requirement to separately install differential interferometers for measuring relative position shifts, in the Y direction, between mask stages and substrate stages at a plurality of positions that are separated in the X direction, costs increase, which has become a problem that cannot be ignored in recent years due to the strong demand for cost reduction.
In view of the aforementioned problems, it is an object of the invention to provide a scanning exposure apparatus, a scanning exposure method and a mask that contribute to cost reduction by reducing the number of measurement axes of the interferometer(s) required to measure the flatness tolerance of long mirrors.
In order to achieve the above and/or other objects, one aspect of the invention relates to a scanning exposure apparatus in which a mask and a substrate such as, e.g., a plate, are moved along a first direction (a scanning direction) to expose a pattern of the mask onto the substrate. The scanning exposure apparatus preferably includes at least a pair of projection optical systems spaced a predetermined distance from each other in the first direction and displaced from each other in a second direction, which is perpendicular to the first direction, such that at least a portion of projection areas where the patterns are projected by the projection optical systems onto the substrate overlap each other. In addition, a shifter is provided to shift images of the overlapping exposure patterns on the substrate along the second direction.
A scanning exposure method according to one aspect of the invention includes the steps of simultaneously moving a mask and a substrate along a first direction while exposing an image of a pattern of the mask onto the substrate. The method further comprises a step of, during exposure to the substrate using a pair of projection optical systems that are spaced from each other in the first (X) direction by a predetermined distance and displaced from each other in a second (Y) direction perpendicular to the first direction such that at least a portion of projection areas where the patterns are projected onto the substrate by the pair of projection optical systems overlap, shifting the overlapping exposure patterns on the substrate along the second direction.
In the scanning exposure apparatus and the scanning exposure method of this aspect of the invention, the mask is positioned in such a manner that a pattern is scanned in the area where the projection areas of the pair of projection optical systems overlap. In addition, when the mask and the substrate are moved along the first direction (X direction), based on respective displacement measured using the long mirrors, after the shifter shifts the imaging position of one of the projection optical systems in the pair of projection optical systems along the second direction (Y direction), the image of the pattern projected by the shifted projection optical system is shifted relative to the image projected by the other projection optical system, and are separated in the second direction (Y direction).
In this process, each projected image is displaced by an amount that depends on the flatness tolerance of each long mirror at each position on which the patterns are projected by each projection optical system. For this reason, a value obtained by subtracting a shift amount from the interval between both projected images is equal to an error produced in the second direction (Y direction) for the position of the patterns formed on the substrate by the pair of projection optical systems, namely the flatness difference between two points of the long mirrors.
In this case, because each separated pattern is projected with half the exposure amount compared to the case in which the patterns are overlappingly projected, it is preferred to have the exposure amount of the projection areas doubled. Moreover, in order to make measurement of the separated patterns easy, it is preferred to shift the imaging position of one of the projection optical systems to avoid overlapping of both projected images.
The mask according to one aspect of the invention has patterns that are projected by a pair of projection optical systems that are spaced from each other in a first direction by a predetermined distance, and the patterns are formed as a plurality of patterns, with the predetermined distance in the first direction between each pattern.
Hence, in the mask of the invention, images projected by each projection optical system are separated from each other (rather than being completely overlapped) by shifting the position (the imaging position) where one of the projection optical systems forms the image on the substrate in the second direction, which is perpendicular to the first direction. Moreover, the value obtained by subtracting a shift amount from the interval between the two separated projection images is equal to a flatness difference between two points of the long mirrors that is produced when the patterns are formed by the pair of projection optical systems onto the substrate during movement of the substrate and the mask.